Spontaneous DNA repair in human peripheral blood mononuclear cells

DNA molecules are constantly damaged during mitosis and by oxygen-free radicals produced by either cellular metabolism or by external factors. Populations at risk include patients with cancer-prone disease, patients under enhanced oxidative stress, and those treated with immunosuppressive/cytotoxic therapy. The DNA repair process is crucial in maintaining the genomal DNA integrity. The aim of this study was to evaluate spontaneous DNA repair capacity of peripheral blood mononuclear cells (PBMC) from normal blood donors. PBMC DNA repair ability represents DNA repair by other tissues as well. It is shown in the present study that in vitro incorporation of [3H]thymidine in non-stimulated PBMC expresses the ability of the cells to repair DNA damage. This method was validated by double-stranded DNA measurements. Both catalase and Fe2+ increased DNA repair, the former by preventing re-breakage of newly repaired DNA and the latter by introducing additional DNA damage, which enhanced DNA repair. Better understanding of DNA repair processes will enable to minimize DNA damage induced by oxidative stress.     

Polymorphism of Unique Noncoding DNA Sequences in Wild and Laboratory Mice

Two DNA probes, D17Tu1 and D17Tu2, were isolated from a genomic DNA library containing only two mouse chromosomes, one of which is chromosome 17, carrying the major histocompatibility complex (H-2), as well as the t complex genes. The D17Tu1 probe was mapped to the centromeric region of chromosome 17 and the D17Tu2 probe to the S region of the H-2 complex. Neither of the two probes appeared to detect any genes, but both contained unique, nonrepetitive sequences. Typing of DNA obtained from a large panel of mice revealed the presence of four D17Tu1 patterns in inbred mouse strains, one very common, one less common, and two present in one strain each. The two common patterns could not be detected in appreciable frequencies in the European wild mice tested (one of the two patterns was, however, found in Australian wild mice). Conversely, the patterns found frequently in European wild mice are absent in the laboratory mice. We therefore conclude that wild mice from the sampled regions of Europe could not have provided the ancestral stocks from which inbred strains were derived. Only one D17Tu1 pattern was found in all the populations of Mus musculus tested, while eight patterns were found in Mus domesticus, with virtually all the populations being polymorphic. We suggest that this difference reflects different modes in which the two species colonized Europe. The distribution of the D17Tu2 patterns in inbred strains correlates with the distribution of H-2 haplotypes.     

Low H-2 polymorphism in some Israeli wild mouse populations

Two populations of the wild house mouse, Mus domesticus, found living close to each other (one inhabited a chicken coop and the other an open field at the Educational Farm of the Hebrew University of Jerusalem, East Talpiot, Jerusalem) were studied for their H-2 polymorphism. These two populations were selected because they are well characterized in terms of their ecological parameters; they have been under continuous surveillance for several years. Twenty-seven H-2 homozygous lines were produced by mating wild mice from these two populations with laboratory strains. The H-2 ^w homozygotes were then characterized by serological typing with monoclonal and polyclonal antibodies specific for the known allomorphs controlled by the class I H-2K and H-2D loci or the class II H-2A and H-2E loci. They were also used as donors for immunizations and for the selection of antisera defining the H-2 haplotypes carried by these lines. Four new H-2 haplotypes could be identified: H-2 ^w82 (K ^wl6 D^ws2) H-2 ^w83 (K ^w83 D^w16) H-2 ^w84 (K ^w84 D^w84) and H-2 ^w85 (K ^w83D^w84) the last haplotype being a recombinant derived from H-2 ^w83 and H-2 ^w84. Antinsera defining the new haplotypes were then used for a study of the wild populations. This study revealed that the populations contain only the four identified H-2 haplotypes, having three alleles at the H-2K locus (K ^w16 K^w83, K^w84) and three alleles at the H-2D locus (D ^w16, D^w82 and D ^w84). The alleles occur in the populations with a frequency of 0.12–0.54. There were no significant differences in gene frequencies between the two populations, and the allele frequencies remained more or less stable. There was a significant excess of heterozygotes for at least some of the genes, compared with the frequency expected from Hardy-Weinberg equilibrium. The same antisera were also used to type other populations in the vicinity of Jerusalem. In one population, located 30 km west of Jerusalem, the mice failed to react with any of the reagents. In the other two populations, located 15 km west and 40 km northeast of Jerusalem, three of the four H-2 haplotypes found in East Talpiot were present at high frequencies. It appears, therefore, that only three main H-2 haplotypes and two or three minor ones are present in the area around Jerusalem. This study thus provides the first example of a large mainland population in which the H-2 polymorphism is comparable to that of many other non-H-2 loci.     

Locating alignments with k differences for nucleotide and amino acid sequences

Given two sequences, a pattern of length m, a text of lengthn and a positive integer k, we give two algorithms. The firstfinds all occurrences of the pattern in the text as long asthese do not differ from each other by more than k differences.It runs in O(nk) time. The second algorithm finds all subsequencealignments between the pattern and the test with at most k differences.This algorithm runs in O(nmk) time, is very simple and easyto program. Received on August 12, 1987; accepted on December 31, 1987     

Breeding systems in thePolemoniaceae

Pollen — ovule ratios and percentages of stigmatic pollen germination (SPG) were measured for over 160 taxa of thePolemoniaceae. When related to taxa with known breeding systems, it is found that low SPGs and high P:O ratios characterize xenogamous plants, high SPGs and low P:Os characterize autogamous plants. There is a significant negative correlation between P:O ratio and SPG in the whole family as well as in certain genera. Both measures can serve as reliable indicators of the breeding systems in taxa of thePolemoniaceae and can be measured in dried or living specimens. Accordingly, most polemons feature mixed breeding system, i.e. facultative xenogamy or facultative autogamy. Xenogamy is common among the tropical genera and in theLeptodactylon, Phlox andPolemonium. Autogamy is more frequent in the tribeGilieae (particularly inGilia) than in the other tribes. Annual taxa tend to be autogamous, showing on the average higher SPG and lower P:O ratio. The lepidopteran-pollinated group of species have a higher mean P:O ratio and lower mean SPG thus indicating that such plants are associated with crosspollination more than the others.     

Maternal Inheritance of Enzymes in the Mealybug PSEUDOCOCCUS OBSCURUS (Homoptera)

In the mealybug Pseudococcus obscurus Essig (Pseudococcidae) two esterases, a tyrosinase and a mannosephosphate isomerase, exhibited an unusual type of maternal inheritance. Electromorphs (alleles) were transmitted by both parent but segregation was delayed by one generation and full sisters always had the same phenotype. Moreover, for esterase-1, in which three alleles were present, some of the females exhibited all three alleles. Several other polymorphic loci exhibited normal transmission and segregation. This mode of inheritance can be readily explained by assuming that most or all of the enzymes coded for by these loci are produced by the mycetocytes. The mycetocytes house intracellular bacteria-like symbionts and are usually formed by the fusion ofthe polar bodies and one or more cleavage nuclei. For a locus with two alleles exhibiting this type of inheritance, the expected frequencies of the three phenotypes are p3, 3pq an equation is presented for estimating the frequency of alleles from the frequencies of the phenotypes and it is shown that for three samples from wild populations there is a good agreement between the expected and observed frequencies of the phenotypes.     

Gonoid thelytoky in soft scale insects (Coccidae: Homoptera)

Cytological analysis of the thelytokous soft-scale insects Coccus hesperidum L. (2n=14) and Saissetia coffeae (Walker) (2n=16) revealed that while in both species the chromosomes did not pair during prophase I, meiosis consisted of two divisions, the chromosome number was reduced, and diploidy was restored by the fusion of the female pronucleus with the polar nucleus II. The difficulty of trying to classify this type of thelytoky as either automictic or apomictic led to the proposal that a new criterion and new terms be used to classify thelytoky (and parthenogenesis). The new criterion is whether the number of chromosome elements present in the first (or only) metaphase of oogenesis is the same as that present in the oogonia (gonoid thelytoky) or different from it (agonoid thelytoky). The new criterion is superior to the existing criteria because it is unambiguous, and because it groups together forms with a similar tendency towards heterozygosity (or homozygosity). The possible evolution of the forms analyzed as well as the two other thelytokous forms of each species described by Thomsen (1927) are discussed. Another soft-scale insect, Physokermes hemicryphus Dalam, consisted of a diploid (2n=18) and a triploid (3n=27) form, in both of which the chromosomes also did not pair. Each of the three species contained a strain in which only a single nucleolus was present per cell. In C. hesperidum some strains with two nucleoli differed in the size of the nucleoli.     

The role of climate,water and biotic interactions in shaping biodiversity patterns in arid environments across spatial scales

Aim

Desert ecosystems, with their harsh environmental conditions, hold the key to understanding the responses of biodiversity to climate change. As desert community structure is influenced by processes acting at different spatial scales, studies combining multiple scales are essential for understanding the conservation requirements of desert biota. We investigated the role of environmental variables and biotic interactions in shaping broad and fine‐scale patterns of diversity and distribution of bats in arid environments to understand how the expansion of nondesert species can affect the long‐term conservation of desert biodiversity.

Location

Levant, Eastern Mediterranean.

Methods

We combine species distribution modelling and niche overlap statistics with a statistical model selection approach to integrate interspecific interactions into broadscale distribution models and fine‐scale analysis of ecological requirements. We focus on competition between desert bats and mesic species that recently expanded their distribution into arid environment following anthropogenic land‐use changes.

Results

We show that both climate and water availability limit bat distributions and diversity across spatial scales. The broadscale distribution of bats was determined by proximity to water and high temperatures, although the latter did not affect the distribution of mesic species. At the fine‐scale, high levels of bat activity and diversity were associated with increased water availability and warmer periods. Desert species were strongly associated with warmer and drier desert types. Range and niche overlap were high among potential competitors, but coexistence was facilitated through fine‐scale spatial partitioning of water resources.

Main conclusions

Adaptations to drier and warmer conditions allow desert‐obligate species to prevail in more arid environments. However, this competitive advantage may disappear as anthropogenic activities encroach further into desert habitats. We conclude that reduced water availability in arid environments under future climate change projections pose a major threat to desert wildlife because it can affect survival and reproductive success and may increase competition over remaining water resources.